FES climb rate at 15kW power?

[Richard DalCanto]

I was looking at the FES manual, and I was curious what climb rates (in ft/min) people are getting in 18M gliders at the recommend sustained climbing power of 15-18kW? Are you getting over 3,500ft of total climbing? I have a JS3 on order with FES sustainer option (because I don't plan on competing at the national level I'm not too worried about losing 2 pts from the folded prop on the nose).
Thanks,
Rick

[[email protected]]

The JS3 has a FES option?

[Per Carlin]

I would say it depends alot on the weight.

To keep hight do you need an force equal to the weight divided by L/D for current speed. For a JS3 at full load would it be something like 600/50 => 12kg
Power is force times speed => 12*9,81(Convert to Newton) * 130(best L/D)/3,6 (convert to m/s) => 12*9,81*130/3,6 => 4,3kW.

You then have about 10kW in exess power to climb: Power = weight * vertical velocity => Climb = 10k / (600 * 9,81) = 1,7m/s

This is teoretical. 15kW is the input to the converter, you loose some % in the electrical system, you also loose alot in the efficienty of the propeller. A good guess is that you have an system efficeiny of about 50%. => climbrate less than 1m/s.

[Shaun Murdoch]

Shark FES (391kg plus me).. around 2-2.5 knots climb at full power.
Battery empty in 7 minutes (apparently). Haven't tried using up the full
capacity for a climb, not been necessary.

It's more efficient to just cruise home with the vario on 0, you'll get a
longer range out of it. Realistically around 70km without terrain or
accounting for headwind. Less if you climb up to an acceptable cruise
alt.


At 23:18 20 January 2019, Richard DalCanto wrote:
>I was looking at the FES manual, and I was curious what climb rates
(in
>ft/=
>min) people are getting in 18M gliders at the recommend sustained
climbing
>=
>power of 15-18kW? Are you getting over 3,500ft of total climbing?
I
>hav=
>e a JS3 on order with FES sustainer option (because I don't plan on
>competi=
>ng at the national level I'm not too worried about losing 2 pts from
the
>fo=
>lded prop on the nose).
>Thanks,
>Rick
>

[Richard DalCanto]

On Sunday, January 20, 2019 at 7:56:54 PM UTC-7, wrote:
> The JS3 has a FES option?

Yes. IT is not obvious on the website. But if you go to FAQ -Engine, you see FES is an option. There are 4 of us with FES on order. Everyone else who is ordering the glider with a sustainer is ordering the jet. Ratio more than 5:1 Jet:FES. The FES is the same system used in LAK, Ventus, etc. I really like the re-designed FES battery and believe that the fire risk is a thing of the past. FES should theoretically be more reliable. The slower flight speed of the FES is a negative, but also a positive in that you can use it at low power to climb faster in a weak thermal when making a save. I imagine it is harder to do that in the Jet going 75+ knots.

[Richard DalCanto]

On Monday, January 21, 2019 at 4:15:04 AM UTC-7, Shaun Murdoch wrote:
> Shark FES (391kg plus me).. around 2-2.5 knots climb at full power.
> Battery empty in 7 minutes (apparently). Haven't tried using up the full
> capacity for a climb, not been necessary.
>
> It's more efficient to just cruise home with the vario on 0, you'll get a
> longer range out of it. Realistically around 70km without terrain or
> accounting for headwind. Less if you climb up to an acceptable cruise
> alt.
>

Interesting. Living in the rockies, just cruising home at 0 may not be an option. May need to use it to climb back into the lift band. The FES manual says that the heavier 18M gliders should get over 3,500 feet of climb in a charge. Are you not seeing that?